The bottom side probably looks great. If you change one of these filters and study the intake box, you will see how debris collects on the top, but falls off on the sides and does not collect on the bottom. And as air filters go, the used stock one in the picture is not bad or clogged up enough to cost 15 hp.

You have not ever changed your filter clearly. Leaves and bigger debree collect on top as its a function of vacuum and gravity that they get sucked and settle on top. The dirt and smaller dust etc is directed from the road with almost a straight shot into the bottom of the intake. The top is getting air from the grilles and the hood vent at high speeds, relatively cleaner air than the road grime.